It is known that certain functions of living organisms and also of electrical and mechanical apparatus, are characterized by events which occur in specific time sequences and that the time relationships among such events are indicative of the satisfactory performance of the functions. Thus, by comparing the times between occurrence of two events characteristic of a function with a statistically normal time for the duration between such events it can be determined whether the function is being properly performed. If the measured time deviates from the normal time, diagnosis as to the cause of malfunction may be made.
One of the many possible areas in which event interval measurement may be employed for monitoring and diagnosis is in the care of the newborn infant. It has been found that electromechanical interval is an excellent indicator of neonatal distress. The electromechanical interval is the time between the myocardial electrical impulse (ECG) transmitted to the neonatal heart, commonly shown on the electrocardiogram, and the onset of the absolute blood pressure pulse resulting from the heartbeat. Although the electrical heart signal causes no problem for detection, this is not true of the blood pressure signal. The blood pressure signal is characteristically a noisy one subject to variations in amplitude and onset slope. It is also affected by variations in the blood pressure base line, i.e., the average blood pressure. Thus, in order to accurately measure the electromechanical interval a method for determining blood pressure pulse onset and apparatus necessary for execution of the method are required.